Our general goal is to find the neuronal basis for the recovery of function after a surgical lesion in the leech central nervous system. More specifically, we are investigating the mechanisms by which a single leech ganglion which has been surgically isolated from the rest of the nervous system acquires the ability, over a two week period, to produce normal swimming activity. We have found many of the neurons responsible for the initiation of swimming and have shown that both morphological and physiological changes occur in the surgically isolated ganglia. In the course of the next year, we plan to pursue four projects: 1. To test electrophysiologically the strength of the connections between pairs of swim-related neurons in chronically isolated ganglia. 2. To determine whether there are anatomical changes in the processes of neurons whose physiological properties change. 3. To see whether sprouting processes in sensory neurons, interneurons, and motor neurons follow one another into new regions of the neuropil. 4. To relate the differences in time course of the behavioral changes induced by nerve cord ablation with the changes in anatomical and physiological properties of the neurons.